1. Field of the Invention
The present invention relates to a gas flow guiding device for use in a crystal-growing furnace, and more particularly, to a gas flow guiding device for use in a crystal-growing furnace that is capable of effectively reducing the impurities present in a crystal ingot produced thereby.
2. Description of the Prior Art
It is known in the art that a solar cell is a non-pollutant renewable energy source that can directly generate electric power by virtue of the interactions between the sunlight and chemical materials. Especially, the solar cell will not discharge any undesired waste gas during use, such as CO2, so that the solar cell is promising in helping environmental protection and solving the problem of the earth's greenhouse effect.
A solar cell is a device that is capable of converting the solar energy into electrical power by generating a potential difference at the P-N junction interface of a semiconductor device, rather than by transmission of electrically conductive ions via an electrolyte. The semiconductor device will generate a tremendous amount of electrons when struck by the sunlight, and the movement of the electrons results in a potential difference at the P-N junction.
The modern solar cells are typically made by three types of materials: amorphous materials, mono-crystal materials and poly-crystal materials. FIG. 1 illustrates a furnace for producing a silicon crystal ingot, which primarily includes a crucible 21 for containing a silicon melt 11. The crucible 21 is provided circumferentially with a lateral insulation layer 22 and an upper insulation layer 23, so as to constitute a hot zone, in which a heater 24 are equipped to provide heat to silicon .
The upper insulation layer 23 is further provided with a gas inlet 25 used for introducing an inert gas, whereas the lateral insulation layer 22 may be formed with a gas exit 26. During the process of melting the silicon by heat, a gas is introduced into the furnace at a predetermined flow rate through the gas inlet 25 to generate a gas flow passing through the hot zone and, thus, carrying the impurity away from the furnace via the gas exit 26.
A crystal ingot 12 may be obtained by reducing the output power of the heater 24 (casting process), or by moving the lateral insulation layer 22 upwards to allow radiant cooling of the crucible 21 (directional solidification system process), to thereby solidify the silicon melt 11 contained within the crucible 21.
Moreover, the crystal ingot 12 may also be obtained by additionally disposing a support 28 between the crucible 21 and a base 27, so that the silicon melt 11 contained within the crucible 21 can be solidified by lowering the support 28 to draw the crucible 21 downwards to a cooling zone (Bridgman process), or by introducing a cooling fluid into the support 28 (heat exchanger process).
In the conventional furnace described above, however, the gas inlet 25 of the gas flow guiding device only slightly protrudes into the hot zone beneath the upper insulation layer 23. As a consequence, the opening of the gas inlet 25 is located so far from the free surface of the silicon melt 11 contained in the crucible 21 (namely, the interface of the silicon melt and the gas) that the gas flow introduced through the gas inlet 25 fails to effectively carry the impurities away from the free surface and leads to an unfavorable result that the crystal ingot produced thereby has a high concentration of impurities and a reduced crystal quality.